The present invention relates to a method for producing a clad steel pipe. Not only pressure tightness and heat resistance, but also corrosion resistance and wear resistance are indispensable to oil pipes or plant transferring pipes. A corrosion-resisting double walled pipe which is constructed of an inner pipe made of stainless steel and an outer pipe made of carbon steel is used for meeting such requirements. Both the inner pipe and the outer pipe should be tightly joined.
In the conventional method for producing this kind of a double walled pipe, the outer pipe is made of carbon steel and the inner pipe is made of stainless steel with both of them being joined by suitable ways such as a pip expansion method using hydro pressure, the edges of the pipe being seal-welded so as not to slide along the axis of the pipe.
A welded pipe was also heated at a high temperature and elongated by using a die and a mandrel or rolled and elongated by drawing.
In the above-mentioned method, however, heating to a high temperature at the time of rolling and application of machine power for, extruding and drawing was required. For instance, in the case of a double walled pipe made of carbon steel and stainless steel, the base pipes have to be kept at 1200.degree. C. for a long time, so that there are disadvantages as regards the maintenance of the heating apparatus and the machinery and the requirement for expensive apparatus itself on a large scale. Furthermore, by using the above-mentioned conventional method, there are difficulties that scar or breakout in a pipe caused by the differences in the ductility and the deformation resistance at a high temperature between the dissimilar base metals which are joined together. Also, the bonding efficiency and the yield of products seem to be unsatisfactory.